1. Field of the Invention
The present invention relates to a screen-type spirometer having an improved pneumotachometer, which has a simple structure and a low manufacturing cost and is convenient to use.
2. Description of the Related Art
Generally, an examination of the capacity of the lungs is a kind of a synthetic lungs function examination, and is used in evaluating all of ventilatory functions and a part of distributive functions among functions of the lungs. In other words, the examination of the capacity of the lungs is a widely-used examination which commands an overwhelming majority in examining the functions of the lungs. The examination of the capacity of the lungs mainly evaluating the ventilatory functions can be applied to examine a respiratory function of a patient having a specific disease or a patient to be undergone an operation. Further, the examination of the capacity of the lungs can be applied to diagnose a health condition of a general person or a sufferer from an industrial disease, etc. At the present time, due to the industrialization, the environmental pollution is growing more and more serious and thereby the number of the sufferer from the industrial disease is rapidly increased. At this point of time, the examination of the capacity of the lungs is regarded as a very important examination.
Generally speaking, two types of pneumotach apparatus have been used in examining the capacity of the lungs. One type of the pneumotach apparatus is an apparatus for quantitatively measuring the capability of lung volume, which is an expansion and a contraction of the lungs. This apparatus directly measures the change of the lung volume while a person to be examined breathes according to a breathing protocol which is arranged beforehand. The other type of the pneumotach apparatus is an apparatus for sensing a fluid flow passing through the lungs inward or outward while the person breathes and for determining the quantity of respiration of the person by integrating the flow measurement values.
In the past, the former apparatus had been mainly used in examining the capacity of the lungs. However, the structure of the former apparatus is relatively complicated and the dynamic response thereof is not satisfactory. Accordingly, at the present time, the latter apparatus has been widely used in examining the capacity of the lungs.
Various types of the latter apparatus have been used for measuring a volume flow of the fluid flow per unit time. The respiratory gas streams at a great volume, and the latter apparatus must continuously measure an absolute quantity of the gas flow flowing in both directions(inspiratory and expiratory) and must provide a relatively accurate flow measurement to an operator thereof regardless of the change of measuring environment. Further, in the use of the latter apparatus, this apparatus must not hinder the respiration of the patient. Therefore, a measuring method of the latter apparatus is limited. Since the latter apparatus must continuously measure the absolute quantity of the fluid flow, it must employ a measuring method indicating an excellent dynamic response.
Pneumotachography, which has been widely used in research and development for respiratory organs, can be employed as the measuring method capable of satisfying the conditions described above. Pneumotachography uses a phenomenon that fluid energy of the respiratory gases is lost due to the friction generated between the fluid flow and a screen acting as a mechanical resistance at the time that the respiratory gases pass through the screen thereby a pressure drop of the fluid flow corresponding to the lost fluid energy is generated. At this time, the pressure drop is associated with the respiratory gas flow. Accordingly, it is possible to calculate a quantity and the flow direction of the respiratory gases by measuring a variance in a respiratory pressure difference on both sides of the screen.
U.S. Pat. No. 5,060,655, issued to Kelvin A. Rudolph on Oct. 29, 1991, discloses a pneumotach apparatus having a pneumotachometer and subsidiary equipments used in conjunction with the pneumotachometer. This pneumotach apparatus uses the respiratory gases measuring manner as described above. In this pneumotach apparatus, the pneumotachmeter includes a passageway and having a plurality of screens disposed within the passageway. The subsidiary equipments of the pneumotach apparatus comprise a pressure transducer which is fluid-communicated with the pneumotachmeter by means of a pair of flexible tubes, and comprise a flow indicating instrument for displaying a flow measurement of the respiratory gases which is connected to the pressure transducer by means of a conduit.
FIG. 5 illustrates schematically a screen-type spirometer according to a prior art, with subsidiary equipments of the spirometer omitted for the sake of clarity. Referring to FIG. 5, a pneumotach apparatus 10 mainly includes a pneumotachometer 12, a screen heater 18, a pressure transducer (not shown) and a flow indicating instrument (not shown). Pneumotachometer 12 is fluid-communicated with the pressure transducer by a pair of flexible tubes 11, 13. Screen heater 18 is electrically connected to pneumotachometer 12 by a cable 17. Screen heater 18 is used for heating a plurality of circularly shaped screens 60a,60b,60c(referred to FIG. 6), which are disposed within a passageway for allowing the respiratory gases to flow therethrough, in order to remove a humidity formed on screens 60a,60b,60c after using pneumotachometer 12. Screen heater 18 includes an on/off switch 18a and a screen temperature setting switch 18b.
FIG. 6 is an enlarged and exploded perspective view of a pneumotachometer illustrated in FIG. 5. Referring to FIG. 6, pneumotachometer 12 includes an annularly shaped first housing 20, an annularly shaped second housing 30, a hollow first tube adapter 40, a hollow second tube adapter 50, screens 60a,60b,60c, an annularly shaped sealing ring 70, a first cover 80 and a second cover 82, a first pressure tap 90 and a second pressure tap 92.
First housing 20 includes a shoulder 21 extending radially outward from an upper portion of first housing 20, a protrusion 22 extending radially outward from at an outer surface of first housing 20, a first female threaded portion 23 formed at an inner lower end of first housing 20 and a second female threaded portion 25 formed at an inner upper end of first housing 20.
Further, a locking groove 24 is vertically formed at an inner surface of first housing 20. A first through hole 26 and a second through hole 27 for receiving first pressure tap 90 and second pressure tap 92, respectively, are formed at protrusion 22 of first housing 20.
When pneumotachometer 12 is assembled at a one body, second housing 30 receives first housing 20. In order to accomplish this task, an annularly shaped second ring 32 of second housing 30 has an inner diameter greater than an outer diameter of an annularly shaped first ring 28 of first housing 20. Cable 17 extending from screen heater 18 (referred to FIG. 5) is connected to a cable connecting portion 31 provided on an outer surface of second housing 30. An aperture 33 is formed at a position of the other surface of second housing 30 which is opposite to cable connecting portion 31. When first housing 20 and second housing 30 are combined with each other, protrusion 22 of first housing 20 is fitted into aperture 33.
An annularly shaped locking portion 34 is formed at an inner lower portion of second housing 30. When first housing 20 and second housing 30 are combined with each other, locking portion 34 supports a bottom outer surface of first housing 20. A metal heating element 36 is installed on an inner surface of second housing 30. Heating element 36 heats screens 60a,60b,60c disposed within first housing 20 at need under the state that first housing 20 and second housing 30 are combined with each other. In other words, when an electric current is applied to heating element 36 from screen heater 18 through cable 17, heating element 36 heats screens 60a,60b,60c.
Screens 60a,60b,60c act as mechanical resistances and are made of stainless steel. A suitable size for screens 60b and 60c among them has been found to be in the range of a screen having a mesh between 100 and 130 openings per inch. On the contrary, a suitable size for main screen 60a has been found to be in the range of a screen having a mesh between 300 and 330 openings per inch. Main screen 60a acts as the substantial mechanical resistance, and screens 60b and 60c stabilize the fluid flow. Screens 60a,60b,60c have screen members 62a,62b,62c for supporting a netting loop of screens 60a,60b,60c, respectively. Locking projections 64a,64b,64c are formed on outer surfaces of main screen 60a and screens 60b,60c, respectively. When main screen 60a and screens 60b,60c are disposed within first housing 20, locking projections 64a,64b,64c are snugly fitted within locking groove 24 formed at the inner surface of first housing 20.
First tube adapter 40 is provided with a first hose receiving portion 42 and an annularly shaped first flange 44. First hose receiving portion 42 receives a hose(not shown) for transferring the respiratory gases which is conventionally used to measure the capacity of the lungs of a patient. First cover 80 can be fitted into a distal end of first hose receiving portion 42. When first tube adapter 40 is engaged with second housing 30, first flange 44 tightly contacts with a bottom outer surface of second housing 30. Meanwhile, a first male threaded portion 46 is formed at an upper end of first tube adapter 40. When first tube adapter 40 is engaged with second housing 30, first male threaded portion 46 is engaged with first female threaded portion 23 of first housing 20 which is fitted into second housing 30.
In the same manner as first tube adapter 40, second tube adapter 50 is provided with a second hose receiving portion 52 and an annularly shaped second flange 54. Second cover 82 can be inserted into a distal end of second hose receiving portion 52. When second tube adapter 50 is engaged with first housing 20, second flange 54 tightly contacts with an upper surface of shoulder 21 of first housing 30. Meanwhile, a second male threaded portion 56 is formed at a lower end of second tube adapter 50. When second tube adapter 50 is engaged with first housing 20, second male threaded portion 56 is engaged with second female threaded portion 25 which is formed at an upper end of the inner surface of first housing 20.
Since pneumotach apparatus 10 constructed as described above is provided with the high-priced screens 60a,60b,60c within pneumotachometer 12, there is a problem that the total manufacturing cost of pneumotach apparatus 10 is too expensive. Further, an internal structure of pneumotach apparatus 10 is relatively complicated and therefore the manufacturing process of pneumotach apparatus 10 is also complicated. In addition, when an inspector or a doctor uses screen heater 18 in order to remove the humidity formed on screens 60a,60b,60c of pneumotachometer 12 after using pneumotach apparatus 10 to a person to be examined, a next person to be examined must wait for a duration of time until the humidity formed on screens 60a,60b,60c are completely removed. Further, any dirts and microorganisms within the humid cannot be removed and can cause a secondary infection, by just heating and drying, to the next person to be examined. In other words, only humidity not dirts is removed by heating the pneumotachometer. Accordingly, it is inconvenient to use pneumotach apparatus 10.